The invention is intended in particular for the metallurgical industry and more precisely for the circular apparatuses included in electroplating manufacturing lines, e.g. of the continuous electro-galvanizing type. Such apparatuses are referred to as "conductor rolls" and are described, for example, in the following U.S. patents: U.S. Pat. No. 3,483,113 (in particular FIGS. 7, 8, and 9), and U.S. Pat. No. 3,634,223.
These conductor rolls act as cathodes and are generally constituted by at least one electrically conductive cylindrical ring, generally made of stainless steel, mounted on a carbon steel body which is wider than the active zone(s) of the ring(s) via which the electric current passes. The steel body is covered, on either side of the active zone(s) with a flexible polymer substance which is both resilient and insulating, said substance serving, where necessary, to provide drive, and also to provide, sealing, electrical insulation, and protection for the body against corrosion. These rolls are partially immersed in an electrolyte which is generally at a temperature higher than ambient.
The strip is wound around a portion of the conductor roll with its inside face that will not be coated being in contact both with the active zone of the conductive ring in order to establish electrical contact, and also with the resilient insulating substance in order to ensure that the contact device is sealed.
It will readily be understood that if the deposit which is electroplated onto the strip as it passes through the electrolyte is to be uniform, then it is essential for the electrical contact between the ring and the strip to be of uniform good quality, for the sealing at the edges of the strip to be of uniform good quality, and also for the current density to be uniform.
The improvements described to such conductor rolls for electroplating in the above-mentioned U.S. patents are generally directed to ensuring that the electrical conduct is of uniform good quality and also to obtaining proper distribution of current density, both of which factors are very important. As to sealing, the bodies of the conductor rolls are generally covered in rubber, neoprene, or similar material, or else in polyurethane, and emphasis is also made on the necessity of using adhesive which are suitable for such resilient sealing strips, given the essential function they also perform in the method.
Special geometrical dispositions are also sometimes provided at the ends of the conductive rings(s) which may be "hollow", "projecting", or "sawtoothed", for the purpose of attempting to increase the reliability of sealing (see FIGS. 4A, 4B, 4C, 4D, and 4E of U.S. Pat. No. 3,634,223).
Further, in order to be sure that the sealing rings perform both the function of sealing and the function of electrical insulation, they are sometimes mounted on a hard insulating band (see FIG. 7 of U.S. Pat. No. 3,483,113).
However, all of these dispositions do not guarantee that electrical contact and the passage of electrical current between the strip and the conducting ring are completely uniform, nor do they guarantee sealing. In all prior dispositions, (and ignoring a thin interface constituted by adhesive), the resilient sealing band comes directly into contact with the side faces of the active zone(s) of the conductive ring(s). This gives rise to various drawbacks:
Given that elastomers expand much more than steel, the effect of increasing temperature is to increase the radial thickness of the resilient band much faster than the radial thickness of the steel, thereby tending to deteriorate the quality and the uniformity of the physical and electrical contact between the strip and the active zone(s) of the conducting ring(s), in spite of the tractive forces exerted on the strip.
Over a period of time, the resilient elastomer band increases in thickness by virtue of being immersed in the electrolyte due to phenomena of absorption and of chemical combination with the electrolyte (a phenomena which is well known to elastomer professionals), thereby further contributing to deteriorating the quality and the uniformity of physical and electrical contact between the strip and the ring(s).
It will readily be understood that such deterioration in the quality and uniformity of contact is particularly damaging at the side edges of the conducting ring(s) since the elastomer (which expands and swells) comes right up to said edges, while in comparison the metal changes very little. Unfortunately, it is specifically in these zones that it is most difficult to ensure that electrical current diffuses properly since the width of the strip to be coated is greater than the width of the conducting ring(s) and it is desirable for the electroplating current density in the strip to be as uniform as possible.
Even though small, this trend towards becoming unstuck has an immediate and large effect from the standpoint of changing electrical resistance, and thus from the standpoint of plating uniformity and installation efficiency. It is therefore common practice to rework the profiles of these resilient bands, which requires the installation to be stopped and disassembled.
Further, these relative movements between the elastomer and the metal end up by degrading elastomer-to-metal adhesion and thus allowing electrolyte to infiltrate between these two component parts, further deteriorating the uniformity of electric current distribution to some extent, and above all corroding the body of the conductor roll.
The object of the present invention is to considerably reduce these drawbacks while ensuring the vital functions of sealing, electrical insulation,and protection of the roll body against corrosion, and also the optional function of drive. another object of the invention is to improve the coatings applied to strips, to improve the energy efficiency of the installation, and to reduce maintenance costs and the frequency with which the installation needs to be stopped.